This invention relates to a novel chip-scale analog beam forming engine for receive array applications consisting of IC chips. The beam forming engine is based upon HRL's Asynchronous Pulse Processor (APP) circuit technology disclosed in U.S. Pat. No. 7,592,939 entitled “Digital domain to pulse domain time encoder” the disclosure of which is hereby incorporated herein by reference. APP involves using Pulse domain processing with time encoders. Pulse processing for other applications is described in other issued US patents assigned to the assignee of the present application, which include: U.S. Pat. Nos. 7,403,144; 7,515,084; 7,724,168; and 7,822,698 for other applications in: frequency filtering (implementing a filter with a given frequency transfer characteristic without beam forming); Analog-to-Digital-Conversion (converting a single analog signal into the digital domain without beam forming); implementation of linear programming circuits (for solving a specific class optimization mathematical problems without beam forming); and implementation of nonlinear processors (for realizing neural networks without beam forming). U.S. Pat. Nos. 7,403,144; 7,515,084; 7,724,168; and 7,822,698 are all incorporated herein by reference,
This invention enables ultra wide bandwidth, low cost and low complexity receive Active Electronically Scanned Arrays (AESA) that are not practical using prior art technologies. Key features of proposed APP-based beam forming engine is that it (1) is scalable up to millimeter wave frequencies and up to extremely large size two- and three-dimensional arrays with arbitrary numbers of independent beams, (2) enables ultra wideband operations with wide instantaneous bandwidth, (3) is affordable since it enables potentially low cost RF CMOS, chip-scale highly modular architectures, (4) is easily extendable to transmit arrays, and (5) provides high Dynamic Range (DR) and linearity operation.
Prior art receive AESA technologies include (a) traditional analog beam forming approaches that utilize conventional phase shifting and time delay devices, (b) element level digital beam forming approaches that utilize a high DR and wide bandwidth Analog-to-Digital Converter (ADC) in each antenna element and (c) subarray level digital beam forming approaches that utilize analog beam forming approaches for the subarrays and use only one ADC for each subarray. Comparison of above array technologies along with the disclosed APP based beam forming approach with respect to required control complexity, Spurious Free Dynamic Range (SFDR) of ADCs, dispersion loss and bandwidth are summarized in Table I below:
TABLE IARRAY CONTROLSFDR & #DISPERSION LOSS &ARCHITECTURECOMPLEXITYOF ADCsBANDWIDTH (BW)Traditional AnalogMediumHigh SFDRHigh LossSmall #of ADCsNarrow BWElement Level Digital HighHigh SFDRHigh LossLarge #of ADCsWide BW(No process gain in SFDR)Subarray Level DigitalHighHigh SFDRHigh LossMedium #of ADCsWide BW(No process gain in SFDR)
Traditional analog beam forming approaches utilize passive or active phase shifters, photonics beam forming approaches that are based upon photonics true time delay elements i.e., long optical cables distributed across the array, and switched transmission lines.
Passive or active phase shifters are inherently narrowband devices that cannot be used for wide bandwidth operation. Also, they are physically large and lossy devices.
In photonics beam forming approach the RF input signals from the antenna elements first need to be converted into optical signals where the beam forming operation is achieved by the delay operation in the optical cables. Then the time delayed optical signals need to be transformed back from optical to RF and need to be digitized and further processed. The RF-to-optical and optical-to-RF transformations are typically lossy processes that require power hungry optical modulator and demodulator devices. Also, a large number of long and precisely cut optical cables are required to obtain fine granulites in the beam angle resolution. While the photonics beam forming based AESA can have wide operational bandwith, its complexity for even medium size arrays is prohibitive. The switched transmission lines beam forming approach requires fast, wide bandwidth and low loss switching devices along with wide bandwith, low loss and long transmission lines. Unfortunately, neither reliable switching devices nor low cost low loss transmission line technology exist today. The RF MEMS switch technology that could provide low loss wide bandwidth RF switches is still in its infancy. Superconductor technology could provide low loss wide bandwidth transmission lines but the cost is prohibitive for all practical applications.
Element level digital beam forming approaches of the prior art utilize a high DR and wide bandwidth Analog-to-Digital Conventer (ADC) in each antenna element. No wideband and high DR (SFDR) ADCs are known by the inventors hereof to exist which makes that prior art approach impractical. No ADCs are required at the antenna elements of the beamformer of the invention.